text: Succinate-CoA ligase is a heterodimer composed of an invariant α-subunit and a substrate-specific ß-subunit, encoded by either SUCLA2 or SUCLG2. This combination results in either an ADP-forming succinate-CoA ligase (A-SUCL, EC 6.2.1.5) or a GDP-forming succinate-CoA ligase (G-SUCL, EC 6.2.1.4). The ADP-forming succinate-CoA ligase is potentially the only matrix enzyme generating ATP in the absence of a proton motive force, capable of maintaining matrix ATP levels under energy-limited conditions, such as transient hypoxia.